C. albicans airway colonization amplifies inflammation in emphysema through the ROS/NLRP3 pathway of macrophages

Objective: In chronic obstructive pulmonary disease (COPD) patients, Candida colonization in the lower respiratory tract is associated with long-term prognosis and acute exacerbations, though the underlying mechanisms remain unclear. This study explores the impact of Candida.albicans (C.albicans) airway colonization on macrophages and airway inflammation in mice with emphysema.

Methods: A chronic emphysema mouse model was established using cigarette smoke and porcine pancreatic Elastase(PPE) exposure. Mice were then instilled with C. albicans spore suspension (5 × 10⁵ CFU/mouse) to induce airway colonization. The Fungal burden in lung homogenates and the body weight change of mice were measured at 24h, 72h, and 120h post installation. At 72h, the Fungal load, alveolar macrophages(AMs) polarization, Reactive Oxygen Species(ROS) content, and NLRP3 and IL-1β expression in the airways or lungs were assessed. In vitro, THP-1-derived macrophages were treated with cigarette smoke extract (CSE), with or without antioxidant inhibitor NAC or NLRP3 Inhibitor MCC950 pretreatment, followed by the stimulation of heat-killed C. albicans (HKCA) spores. The ROS production, NLRP3, and IL-1β protein expression in cells were detected.

Results: After instilling C. albicans into the airways, the body weight changes of the mice were less than 20 % at 24h, 72h, and 120h. Fungal spores are mainly concentrated in the airways, and no spores or hyphae were detected in the alveoli or lung interstitium. The Fungal load decreased by 2.5 log units at 72h. C. albicans colonization enhanced CD86, CD206, and ROS fluorescence in alveolar macrophages, increased IL-1β levels in bronchoalveolar lavage fluid (BALF), and upregulated NLRP3 and IL-1β transcription in lung tissue. In THP-1-derived macrophages, HKCA following CSE stimulation increased CD86, CD206, ROS, NLRP3, and IL-1β levels. ROS inhibition with NAC or NLRP3 inhibition with MCC950 downregulated NLRP3 and IL-1β production.

Conclusion: C. albicans airway colonization promotes macrophage polarization and intensifies inflammation, especially in emphysema mice. ROS production in macrophages may activate NLRP3, leading to increased IL-1β release, which could be a potential mechanism for exacerbating inflammation.

Candida; Chronic obstructive pulmonary disease; Macrophages; NLRP3; Reactive oxygen species.